Multilayer optical disc having pregroove modulation

ABSTRACT

A record carrier is for recording information by writing marks in a track. The record carrier has at least a first recording layer ( 40 ) and a second recording layer ( 41 ). Each layer has a pregroove ( 14 ) indicating the position of the track and exhibiting a wobble modulated for representing physical address information. In addition the pregroove has a pregroove modulation ( 13 ) consituted by variations of a physical parameter related to the shape of the pregroove for encoding axiliary control information. In a scanning device the pregroove modulation is detected in the main detector signal by variations of the reflected radiation.

The invention relates to a record carrier of a writable type forrecording information by writing marks in a track.

The invention further relates to a device for scanning the recordcarrier and a method for providing information via the record carrier.

An optical record carrier is known from WO00/43996. The record carriercomprises a guide groove, usually called pregroove, for indicating theposition of tracks in which the information is to be represented in apredefined manner by recording optically readable marks. The pregrooveis meandering by a periodic excursion of the track in a directiontransverse to the longitudinal scanning direction (further denoted aswobble). The wobble comprises a wobble modulation, for example byinversing wobble periods in phase according to additional informationsuch as physical addresses or recording control information. A scanningdevice is provided with a head for generating a beam of radiation forscanning the track. The marks are detected during said scanning byvariations of the reflectivity of the scanned surface. The variations inintensity of the reflected radiation are detected by a main detectorsystem. Furthermore the scanning device has auxiliary detectors forgenerating tracking servo signals based on the pregroove for detecting aspatial deviation of the head with respect to the track. The trackingservo signals are used to control actuators to position the head on thetrack. The wobble modulation is detected via the auxiliary detectors anddemodulated for retrieving the physical address information. A problemof the known record carrier and device is that the data capacity of thewobble modulation available for encoding control information is limited.

Therefore it is an object of the invention to provide a record carrierand a scanning device for accommodating additional control informationat a higher data capacity.

According to a first aspect of the invention the object is achieved witha record carrier of a writable type for recording information by writingmarks in a track on a recordable area of a recording layer via a beam ofradiation entering through an entrance face of the record carrier, themarks being detectable during scanning the track via the beam by a firsttype of variations of the radiation, the record carrier comprising atleast a first recording layer and a second recording layer, the firstrecording layer being present at a position closer to the entrance facethan the second recording layer, and at least one transparent spacerlayer between the recording layers, and each layer comprising apregroove indicating the position of the track, the pregroove exhibitinga wobble constituted by displacements of the pregroove in a directiontransverse to the longitudinal direction of the track, the wobbleexhibiting a wobble modulation for representing physical addressinformation indicating the physical position of the physical addresswith respect to a starting point of the track and the pregrooveexhibiting a pregroove modulation constituted by variations of aphysical parameter related to the shape of the pregroove, the pregroovemodulation representing auxiliary control information, the wobblemodulation being detectable during said scanning by a second type ofvariations of the radiation and the pregroove modulation beingdetectable during said scanning by further variations of said firsttype.

According to a second aspect of the invention the object is achievedwith a device for scanning a track on the above mentioned record carriervia a beam of radiation, the device comprising a head for providing thebeam, a front-end unit for generating a scanning signal for detectingmarks in the track by detecting scanning signal variations due to afirst type of variations of the radiation, wobble detection means forretrieving the physical address information from the wobble modulationby detecting a second type of variations of the radiation, and pregroovedemodulation means for retrieving the auxiliary control information fromthe pregroove modulation on the first and the second recording layer bydetecting further scanning signal variations due to the first type ofvariations of the radiation.

The effect of the measures is that in addition to the wobble modulationa second, different modulation of the pregroove is available foraccommodating auxiliary control information. This has the advantage thata relatively large capacity for storing auxiliary control data iscreated, e.g. around 1 bit for each wobble period. It is to be notedthat traditional wobble modulation as described for example in WO0/43996may require up to 100 wobble periods for transferring a single bit ofadditional control information. Hence the recording device according tothe invention will read the necessary control data in a much shortertime than control data accommodated in the traditional wobblemodulation, which increases the speed of a startup procedure afterinserting the record carrier.

The invention is also based on the following recognition. The wobblemodulation is suitable for physical address information because suchaddress information is used for locating data sectors (to be) recordedin the track, while the wobble period itself is used for synchronizationof speed of rotation and/or of the recording process. Althoughtraditionally some additional data can be accommodated also in thewobble modulation, the need for auxiliary control information hasincreased greatly in modern recording systems, in particular for highdensity and multilayer recording systems. The inventors have seen thatapplying the pregroove modulation which is detectable via the maindetector and scanning signal the data capacity can be increasedsignificantly, in particular by using both recording layers.

In an embodiment of the record carrier the pregroove modulationcomprises pregroove land areas of zero depth alternating with pregroovepit areas of a predefined depth and width for constituting a pattern ofpregroove marks representing the auxiliary control information. This hasthe advantage that the pattern is produced during manufacture of therecord carrier using the same production steps already used forproducing the pregroove.

In an embodiment of the record carrier said marks in the track havelengths corresponding to an integer number of channel bit lengths T andthe shortest marks having a length of a predefined minimum number d ofchannel bit lengths T for being detectable via a scanning spot having aneffective diameter constituted by said beam on the track, and thepregroove modulation is constituted by a carrier pattern of longpregroove marks, the long pregroove marks having lengths of at least twotimes the predefined minimum number d of channel bit lengths T for beingsubstantially longer than the effective diameter of the scanning spot.The effect of using the long pregroove marks is that a focus offset isdetectable based on the maximum amplitude of the scanning signal.Advantageously adjusting the focus and retrieving the auxiliaryinformation are based on the same area having the pregroove modulation,which increases the startup speed of a device after inserting a recordcarrier. Surprisingly the focus offset so detected correspondssubstantially to the optimum focus offset for reducing errors duringreading or recording the marks. The long pregroove marks aresubstantially longer than the effective diameter of the scanning spot,which effective diameter is effective for reading out marks from atleast a predefined minimum size, and is usually defined as the diameterat which the intensity of radiation is down 50% of its peak value.Advantageously only the focus area having the carrier pattern of longmarks is needed for maximizing the amplitude during offset adjustment.

In an embodiment of the record carrier each recording layer comprises adisc information area in which area the pregroove exhibits saidpregroove modulation, the disc information area being substantiallysmaller than the recordable area of the recording layer, and inparticular the disc information areas of the recording layers beinglocated at corresponding radial positions. This has the advantage thatdisc information is available for each recording layer individually.Advantageously locating the information areas at corresponding positionsreduces the read-out time of the auxiliary control information, becausethe read head does not need to jump radially when switching layers.

Further preferred embodiments of the record carrier and device accordingto the invention are given in the further claims.

These and other aspects of the invention will be apparent from andelucidated further with reference to the embodiments described by way ofexample in the following description and with reference to theaccompanying drawings, in which

FIG. 1 a shows a disc-shaped record carrier (top view),

FIG. 1 b shows a cross-section taken of the record carrier,

FIG. 1 c shows an example of a wobble of the track,

FIG. 1 d shows a wobble having a pregroove modulation by variations ofthe width,

FIG. 1 e shows a wobble having a pregroove modulation by variations ofthe depth,

FIG. 2 shows a scanning device having pregroove demodulation,

FIG. 3 shows a multilayer optical disc,

FIG. 4 shows the focus error signal S-curve,

FIG. 5 shows a modulated wobble, a pregroove modulation and a readsignal,

FIG. 6 shows ADIP information in wobble modulation, and

FIG. 7 shows a wobble demodulation unit.

In the Figures, elements which correspond to elements already describedhave the same reference numerals.

FIG. 1 a shows a disc-shaped record carrier 11 having a track 9 and acentral hole 10. The track 9 is arranged in accordance with a spiralpattern of turns constituting substantially parallel tracks on aninformation layer. The record carrier may be an optical disc having aninformation layer of a recordable type. Examples of a recordable discare the CD-R and CD-RW, and the DVD+RW. The track 9 on the recordabletype of record carrier is indicated by a pre-embossed track structureprovided during manufacture of the blank record carrier, for example apregroove. Recorded information is represented on the information layerby optically detectable marks recorded along the track. The marks areconstituted by variations of a first physical parameter and thereby havedifferent optical properties than their surroundings. The marks aredetectable by variations in the reflected beam, e.g. variations inreflection.

FIG. 1 b is a cross-section taken along the line b-b of the recordcarrier 11 of the recordable type, in which a transparent substrate 15is provided with a recording layer 16 and a protective layer 17. Thetrack structure is constituted, for example, by a pregroove 14 whichenables a read/write head to follow the track 9 during scanning. Thepregroove 14 may be implemented as an indentation or an elevation, ormay consist of a material having a different optical property than thematerial of the pregroove. The pregroove enables a read/write head tofollow the track 9 during scanning. A track structure may also be formedby regularly spread sub-tracks which periodically cause servo signals tooccur. The record carrier may be intended to carry real-timeinformation, for example video or audio information, or otherinformation, such as computer data.

FIG. 1 c shows an example of a wobble of the track. The Figure shows aperiodic variation of the lateral position of the track, also calledwobble. The variations cause an additional signal to arise in auxiliarydetectors, e.g. in the push-pull channel generated by partial detectorsin the central spot in a head of a scanning device. The wobble is, forexample, frequency modulated and position information is encoded in themodulation. A comprehensive description of the prior art wobble as shownin FIG. 1 c in a writable CD system comprising disc information encodedin such a manner can be found in U.S. Pat. No. 4,901,300 (PHN 12.398)and U.S. Pat. No. 5,187,699 (PHQ 88.002).

During readout by scanning the wobble modulation is detectable via asecond type of variations of the radiation, such as variation ofintensity in the cross section of the reflected beam detectable bydetector segments or additional detectors for generating tracking servosignals. Detecting the wobble for a tracking servo system is well knownfrom the above mentioned CD-R and CD-RW system. The wobble modulation isused to encode physical addresses, for example as shown in FIG. 6, whilewobble demodulation is shown in FIG. 7.

User data can be recorded on the record carrier by marks having discretelengths in unit called channel bits, for example according to the CD orDVD channel coding scheme. The marks are having lengths corresponding toan integer number of channel bit lengths T. The shortest marks that areused have a length of a predefined minimum number d of channel bitlengths T for being detectable via the scanning spot on the track thathas an effective diameter, usually being roughly equal to the length ofthe shortest mark.

According to the invention the record carrier has an auxiliary controlarea 12 in which the pregroove is modulated for encoding auxiliarycontrol information. In the auxiliary control area 12 the pregrooveexhibits a pregroove modulation constituted by variations of a physicalparameter related to the shape of the pregroove for representingauxiliary control information. The pregroove modulation is detectableduring said scanning by variations of the reflected beam similar to thevariations due to the marks in the track that are detectable byvariations in the reflected beam, e.g. further variations in reflection.

In an embodiment the auxiliary control area 12 is located at apredefined position on the recording layer. The predefined position isindicated schematically as a part of the track 9 by the rectangle 12 inthe Figure, but in practice the auxiliary control area 12 has sufficientlength for allowing the auxiliary control information to be encoded,e.g. a few windings of the track. In particular the predefined positionmay cover a predefined radial range to allow a device to locate the areabased on the radial positioning of the optical head without the need toread the addresses in the track.

In an embodiment the auxiliary control area 12 is also arranged as afocus area provided for performing a focus adjustment procedure asdiscussed below for setting a best focus offset, which results in a lowjitter in the read-out signal of the user data. The focus area isprovided with a carrier pattern of long marks during manufacture of therecord carrier. The carrier pattern is a series of prewritten marks thatare long compared to the length of the shortest mark used for user dataencoding for being substantially longer than the effective diameter ofthe scanning spot. In particular the long pregroove marks have lengthsof at least two times the predefined minimum number d of channel bitlengths T. The carrier pattern may be constituted by long pregroovemarks having a single length, or may be a predefined pattern using a fewlengths, or may be randomly varied or may be modulated for encoding theauxiliary control information.

In an embodiment of the invention the shortest marks for recording themain information have a length of a 3 channel bit lengths, usuallydenoted as d=3 T or 31. For example in DVD the channel code is an RLL(2,10) code having a minimum length of 3 T, and a maximum length of 11T, while marks of 14 T are used for synchronization. In such a systemthe long marks have at least a length of 6 T or 7 T, but preferably havelengths of at least 8 T. A practical single tone carrier pattern haslong marks of a single size, e.g. pits and intermediate lands having alength of 11 T. It is noted that for a wobble corresponding to apredefined number of channel bit lengths suitable pregroove mark lengthsare selected to constitute a pattern fitting that predefined number. Fora wobble of 32 channel bits like in DVD+RW, a suitable length is 8 Tpregroove pits alternating with 8 T pregroove lands. Suitable ranges oflengths for encoding information in the long marks are a range of 6 T to14 T, or 10 T to 12 T.

According to the invention the pregroove is provided with a pregroovemodulation constituted by variations of a physical parameter related tothe shape of the pregroove as discussed below. The pregroove modulationencodes auxiliary control information such as auxiliary controlinformation. It is noted that the auxiliary information may be used forcontrol information that is processed in the scanning apparatus or ahost computer, e.g. a code for accessing recorded information, anidentifier to support copy-control, anti-piracy information and otheraccessing mechanisms. The control information in the additional datachannel may represent a unique identification code, to protect illegalcopying or a watermark. In an embodiment additional information is madeavailable for the user. The additional information may be a softwareprogram, e.g. for processing, de-compressing or editing audio or videomaterial, or a ‘freeware’ type version of a software program for theuser to try out the functions of said software. In an embodiment theadditional information is audio or video content information, such as atrailer of a movie or an MP3 version of some audio. The user may beinterested in a full version of the movie or audio. A provider may makeavailable such full versions, e.g. via the internet, which versions canthen be downloaded to the record carrier and recorded thereon. Actuallyretrieving and accessing the full versions from record carrier iscontrolled via access codes also included in the pregroove modulation.For example the provider may offer to the user the trailer of a fewmovies or software programs, e.g. 5, and allow the user to record onlyone of them. The user then pays for one movie when buying the recordabledisc. Hence a content provider sells the record carrier with one or moresamples of content information, and makes full versions of said samplesavailable to a user, in particular via a network like the internet.

FIG. 1 d shows a wobble having a pregroove modulation by variations ofthe width. The Figure shows the wobbled pregroove 14 having a pregroovemodulation 13. The shape of the pregroove, being the localcross-sectional shape, is changed according to an additional informationsignal to be encoded. Such change in shape affects the radiationreflected from the track during scanning, and can be detected thereby.As shown in the Figure the width of the pregroove is modulated accordingto a digital modulation pattern.

FIG. 1 e shows a wobble having a pregroove modulation by variations ofthe depth. As shown the depth is varied digitally for constitutingpregroove pit areas 18 having a predefined depth and pregroove landareas 19 having a zero depth (i.e. no pregroove is present). Othervariations of depth may be used instead.

For manufacture of such a record carrier a master disc is made. Duringthe mastering process, the pregroove is written by a laser beamrecorder. The wobble is made by imposing a small lateral offset of thenominal centre position of the track, and the intensity of the laserpower of the mastering laser beam is further modulated to provide thepregroove shape modulation.

The pregroove (width, depth) modulation along the track is used togenerate an additional data channel. The unrecorded disc (R or RW type)then contains additional mastered data, for example recording controldata. The auxiliary data may be encoded using a channel code similar orequal to the channel code used to encode the main user data. This hasthe advantage that no additional circuitry is needed for decoding theadditional data. In an embodiment a different modulation is used, i.e. achannel modulation code differing from the channel code used to encodethe main user data. This allows any modulation to be used for encodinginformation in the pregroove that is optimized for not disturbing theother properties of the pregroove, e.g. a modulation having ‘constantlength pulses’ encoding the additional data by the position of thepulses. Main user data, also called high-frequency data, may besuperimposed on the modulated pregroove. The additional data in thepregroove can be run length-modulated, frequency-modulated,amplitude-modulated, phase-modulated, or any other modulation scheme,which ever is best to distinguish the data from superimposedhigh-frequency main user data.

In an embodiment of the record carrier of the DVD+R or +RW type thepregroove modulation is applied in a guard or buffer zone in the lead-inzone (other places could be lead out zone and middle zone in dual-layerDVD+R or dual-layer DVD+RW). The continuous pregroove is replaced bypregroove pits and lands of either a single tone or multiple tones. Itis noted the ADIP information obtained from the groove is still presentand can be read. As an example a two-layer Opposite Track Path DVD+Rdisc is used. The pregroove pits and lands are placed in the guard zone3 of the lead in zone of the L0 disc (closest to the laser) and in thelead out zone of the L1 layer (below the lead-in zone of the L0 disc).

In an embodiment of the record carrier windings of the track having thepregroove modulation are alternated with windings of the track having nopregroove modulation or having a different, predefined pregroovemodulation. By such a pattern the so-called wobble beat and/or crosstalkof adjacent grooves can be minimized.

FIG. 2 shows a scanning device having pregroove demodulation. The deviceis provided with means for scanning a track on a record carrier 11 whichmeans include a drive unit 21 for rotating the record carrier 11, a head22, a servo unit 25 for positioning the head 22 on the track, and acontrol unit 20. The head 22 comprises an optical system of a known typefor generating a radiation beam 24 guided through optical elementsfocused to a radiation spot 23 on a track of the information layer ofthe record carrier. The radiation beam 24 is generated by a radiationsource, e.g. a laser diode. The head further comprises (not shown) afocusing actuator for moving the focus of the radiation beam 24 alongthe optical axis of said beam and a tracking actuator for finepositioning of the spot 23 in a radial direction on the center of thetrack. The tracking actuator may comprise coils for radially moving anoptical element or may alternatively be arranged for changing the angleof a reflecting element. The focusing and tracking actuators are drivenby actuator signals from the servo unit 25. For reading the radiationreflected by the information layer is detected by a detector of a usualtype, e.g. a four-quadrant diode, in the head 22 for generating detectorsignals coupled to a front-end unit 31 for generating various scanningsignals, including a main scanning signal 33 and error signals 35 fortracking and focusing. The error signals 35 are coupled to the servounit 25 for controlling said tracking and focusing actuators. The errorsignals 35 are also coupled to a wobble demodulation unit 36 forretrieving the physical addresses from the wobble modulation. A detailedembodiment of wobble detection is given in FIG. 7. The main scanningsignal 33 is processed by read processing unit 30 of a usual typeincluding a demodulator, deformatter and output unit to retrieve theinformation.

The control unit 20 controls the scanning and retrieving of informationand may be arranged for receiving commands from a user or from a hostcomputer. The control unit 20 is connected via control lines 26, e.g. asystem bus, to the other units in the device. The control unit 20comprises control circuitry, for example a microprocessor, a programmemory and interfaces for performing the procedures and functions asdescribed below. The control unit 20 may also be implemented as a statemachine in logic circuits. In an embodiment the control unit performsthe functions of retrieving the additional information from thepregroove via the read processing unit 30.

The device has a pregroove demodulation unit 32 for detecting pregroovemodulation in the scanning signal as follows. The main scanning signal33 is received from the front-end unit 31. Components in the signal 33due to the marks of the main information are removed and components dueto the marks of the pregroove modulation are isolated. In an embodimentthe demodulation unit has a filter unit 34 that has a low pass or bandpass function specifically tuned to the long marks. Auxiliary controlinformation is retrieved from the pregroove modulation by the pregroovedemodulation unit 32. Timing recovery for reconstructing a data clock ofthe auxiliary signal can be based on the wobble frequency or on thepregroove modulation itself. In an embodiment timing recovery is basedon the data clock retrieved for the main data. Synchronous detection canbe applied for detecting the data bits of the auxiliary data. In anembodiment the pregroove modulation is provided with a channel codeand/or error correction codes different from the channel codes used inthe user data, and the demodulation unit 34 is provided with a dedicatedchannel code demodulator and/or error correction unit

In an embodiment the device is provided with recording means forrecording information on a record carrier of a writable or re-writabletype, for example CD-R or CD-RW, or DVD+RW or BD. The recording meanscooperate with the head 22 and front-end unit 31 for generating a writebeam of radiation, and comprise write processing means for processingthe input information to generate a write signal to drive the head 22,which write processing means comprise an input unit 27, a formatter 28and a modulator 29. For writing information the beam of radiation iscontrolled to create optically detectable marks in the recording layer.The marks may be in any optically readable form, e.g. in the form ofareas with a reflection coefficient different from their surroundings,obtained when recording in materials such as dye, alloy or phase changematerial, or in the form of areas with a direction of polarizationdifferent from their surroundings, obtained when recording inmagneto-optical material.

Writing and reading of information for recording on optical disks andformatting, error correcting and channel coding rules are well-known inthe art, e.g. from the CD or DVD system. In an embodiment the input unit27 comprises compression means for input signals such as analog audioand/or video, or digital uncompressed audio/video. Suitable compressionmeans are described for video in the MPEG standards, MPEG-1 is definedin ISO/IEC 11172 and MPEG-2 is defined in ISO/IEC 13818. The inputsignal may alternatively be already encoded according to such standards.

FIG. 3 shows a multilayer optical disc. L0 is a first recording layer 40and L1 is a second recording layer 41. A first transparent layer 43covers the first recording layer, a spacer layer 42 separates bothrecording layers 40,41 and a substrate layer 44 is shown below thesecond recording layer 41. The first recording layer 40 is located at aposition closer to an entrance face 47 of the record carrier than thesecond recording layer 41. A laser beam is shown in a first state 45focused on the L0 layer and the laser beam is shown in a second state 46focused at the L1 layer. Each recording layer has the pattern ofpregroove marks that encodes auxiliary control information.

Multilayer discs are already available as read-only pre-recorded discs,such as DVD-ROM or DVD-Video. A dual layer DVD+R disc has recently beensuggested, which disc should preferably be compatible with the duallayer DVD-ROM standard. The reflection levels of both layers are >18%.The L0 layer has a transmission around 50-70%. A spacer layer separatesthe layers with a typical thickness between 30 and 60 μm. The L1 layerhas a high reflection and needs to be very sensitive. Also rewritabledual-layer discs are proposed. The L0 layer has a transmission around40-60%. The effective reflection of both layers is typically 7% althoughlower and higher values are possible (3%-18%). Writable and rewritableoptical storage media having 3 or more recording layers are consideredalso.

FIG. 4 shows the focus error signal S-curve. The focus error signal 48is shown for a focus varied from below to above a recording layer. Forexample in single layer +RW and ROM, the optimal focus-offset is foundby keeping the focus-error at the zero crossing 49 of the S-curve.Additional fine-tuning may be provided by optimizing on pre-recordeddata (in the case of the ROM disc). In dual layer DVD-ROM (DVD-9), theoptimal focus-offset is found by keeping the focus-error at the zerocrossing of the S-curve and then further optimizing on jitter. Here, theoptimal focus-offset suffers from stray light from the other out-offocus layer and/or and from optical aberrations due to the non-idealdepth of the in-focus layer but this can be compensated by optimizing onjitter. In dual layer DVD+R/+RW no pre-recorded data is available tooptimize the jitter values.

In an embodiment the device has a focus adjustment function included inthe focus servo unit 25. First a focus area constituted by an area ofthe pregroove having the pregroove modulation is detected. Then the bestfocus is detected by scanning the carrier pattern in the focus area andmonitoring the amplitude of the scanning signal due to said long marks.In particular a maximum of the amplitude is found by varying the focusoffset. The focus adjustment unit may also be implemented as a softwarefunction in the control unit 20, using the read circuitry available inthe read unit 30 for detecting the amplitude of the signal due to thelong pregroove marks. In an embodiment the focus adjustment function isperformed for a multilayer disc for each of the relevant layersseparately. The focus area on the respective layer is located, and thefurther steps are performed as indicated above for the first layer.Finding the right focus offset is important for writing recordable andrewritable discs. With a non-optimal focus offset the data is written onthe disc in a non-optimal manner, leading to increased write power andjitter values (especially during read out).

FIG. 5 shows a modulated wobble, a pregroove modulation and a readsignal. The x-axis shows time and the y-axis shows the signal values. Anupper curve 51 shows the wobble as a signal deviating in a radialdirection from a nominal zero position. The phase of the wobble ismodulated for encoding physical addresses as indicated by the phasereversal 52. The wobble modulation represents physical addressinformation indicating the physical position of the respective physicaladdress with respect to a starting point of the track The wobblemodulation is known for example from DV+RW and is described in detail inWO00/43996. According to the invention the pregroove constituting thewobble is modulated by alternating pregroove land areas 53 and pregroovepit areas 54. The lower curve 56 shows the resulting read signal usuallycalled central aperture (CA) signal generated by a detector in the readhead. The signal is caused by the difference in reflection of pregroovepits (groove reflection level) and pregroove lands (mirror typereflection level). The signal is comparable to the difference inreflection between a groove and a mirror area on the disc (typically10-15% of the reflection level). Alternatively other methods can beemployed for read out, e.g. radial and tangential push pull. It is notedthat the wobble period or modulation cannot be detected from the CA readsignal, but the pregroove land areas 53 result in pulses 55 in the CAsignal, while the intermediate signal parts 57 are interpreted as beingdue to pregroove pits. Demodulating the pregroove signal elements 55, 57due to the pregroove modulation is relatively straightforward. In anembodiment the pregroove signal elements are directly linked to thewobble PLL clock. Simple filtering and threshold detection can beemployed. When the pits are large (>8 T), inter symbol interference isnegligible and the frequency and the magnitude of the signal are fixed.Channel bits demodulated from the signal are decoded to the auxiliaryinformation according to a channel coding algorithm, for example thesame channel coding as used for the main data in the CD or DVD system.In an embodiment a dedicated channel coding algorithm is used forencoding the auxiliary information in the pregroove land and pit areas,which algorithm for example only uses pregroove mark lengths of 10 to 14channel bits.

In an embodiment the pregroove modulation is aligned with the wobblemodulation. As shown in FIG. 5 the pregroove pit and land areas arealigned to the sine wave shape of the wobble. The lengths of thepregroove marks are selected to allow pregroove modulation patterns thatfit within the lengths of the wobble period. Alternatively the pregroovemodulation is aligned to wobble parts that constitute critical elementsof the wobble modulation like the phase reversal 52, in particular suchcritical wobble parts not containing pregroove modulation.

FIG. 6 shows ADIP information in wobble modulation. The wobblemodulation encodes additional information that is called Address InPregroove (ADIP) in the DVD+RW system. Each ADIP bit 65 is constitutedby ADIP bit sync (one wobble period 64 corresponding to 32 channelbits), followed by a ADIP word sync field (3 wobble periods) and theADIP Data-bit field of 4 wobble periods, followed finally by 85 monotone(i.e. not modulated) wobble periods. The Figure shows a first wobble 61which is encoded as an ADIP word sync, in which the word sync field hasinverted wobbles and the data-bit field has non modulated wobbles.Second wobble 62 encode a data bit value 0 and third wobble 63 encodes adata bit of value 1.

FIG. 7 shows a wobble demodulation unit. The input unit 71 provides apush-pull signal derived from the head scanning the track. A filter 72filters the signal by high pass and low pass filters for isolating thewobble frequency and generating a wobble signal. A phase locked loop 73is locked to the wobble frequency, and generates via a 32× multiplier 75the synchronous write clock for recording marks in units of channelbits. A synchronous wobble unit 74 provides a wobble clock period tomultiplier 76 which also receives the wobble signal. The output of themultiplier 76 is integrated in integrate and dump unit 77, of which theoutput is samples via a sample switch to a sync threshold detector 78coupled to a ADIP bit synchronizer that detects the ADIP bit syncs. Asecond multiplier 81 is provided with a 4 wobble period signal havingtwo inverted and two non inverted wobbles and the wobble signal on asecond input for synchronous detection over 4 wobble periods. A secondintegrate and dump unit 82 integrates output signal of the multiplier82, while a bit value threshold detector 83 for detecting the values ofthe encoded bits.

Although the invention has been mainly explained by embodiments usingoptical discs based on change of reflection, the invention is alsosuitable for other record carriers such as rectangular optical cards,magneto-optical discs or any other type of information storage systemthat has a pre-applied pattern on a writable record carrier. It isnoted, that in this document the word ‘comprising’ does not exclude thepresence of other elements or steps than those listed and the word ‘a’or ‘an’ preceding an element does not exclude the presence of aplurality of such elements, that any reference signs do not limit thescope of the claims, that the invention may be implemented by means ofboth hardware and software, and that several ‘means’ or ‘units’ may berepresented by the same item of hardware or software. Further, the scopeof the invention is not limited to the embodiments, and the inventionlies in each and every novel feature or combination of featuresdescribed above.

1. Record carrier of a writable type for recording information bywriting marks in a track on a recordable area of a recording layer via abeam of radiation entering through an entrance face of the recordcarrier, the marks being detectable during scanning the track via thebeam by a first type of variations of the radiation, the record carriercomprising at least a first recording layer (40) and a second recordinglayer (41), the first recording layer being present at a position closerto the entrance face than the second recording layer, and at least onetransparent spacer layer (42) between the recording layers, and eachlayer comprising a pregroove (14) indicating the position of the track,the pregroove exhibiting a wobble constituted by displacements of thepregroove in a direction transverse to the longitudinal direction of thetrack, the wobble exhibiting a wobble modulation for representingphysical address information indicating the physical position of thephysical address with respect to a starting point of the track and thepregroove exhibiting a pregroove modulation (13) constituted byvariations of a physical parameter related to the shape of thepregroove, the pregroove modulation representing auxiliary controlinformation, the wobble modulation being detectable during said scanningby a second type of variations of the radiation and the pregroovemodulation being detectable during said scanning by further variationsof said first type.
 2. Record carrier as claimed in claim 1, whereinsaid first type of variations are variations of a reflection level ofthe track for the radiation.
 3. Record carrier as claimed in claim 1,wherein the pregroove modulation is constituted by variations of thedepth or width of the pregroove.
 4. Record carrier as claimed in claim3, wherein the pregroove modulation comprises pregroove land areas (19)of zero depth alternating with pregroove pit areas (18) of a predefineddepth and width for constituting a pattern of pregroove marksrepresenting the auxiliary control information.
 5. Record carrier asclaimed in claim 1, wherein said marks in the track have lengthscorresponding to an integer number of channel bit lengths T and theshortest marks having a length of a predefined minimum number d ofchannel bit lengths T for being detectable via a scanning spot having aneffective diameter constituted by said beam on the track, and thepregroove modulation is constituted by a carrier pattern of longpregroove marks, the long pregroove marks having lengths of at least twotimes the predefined minimum number d of channel bit lengths T for beingsubstantially longer than the effective diameter of the scanning spot.6. Record carrier as claimed in claim 5, wherein the predefined minimumnumber d is 3 channel bit lengths T (d=3 T), and the long marks havelengths of at least 6 T, in particular the lengths being in the range of8 T to 14 T.
 7. Record carrier as claimed in claim 4, wherein thepregroove modulation is representing the auxiliary control informationencoded by the pregroove marks according to a predefined channel codingalgorithm, which predefined channel coding algorithm differs from achannel coding algorithm for encoding the information in the marks inthe track.
 8. Record carrier as claimed in claim 1, wherein thepregroove modulation is aligned with the wobble modulation.
 9. Recordcarrier as claimed in claim 1, wherein each recording layer comprises adisc information area (12) in which area the pregroove exhibits saidpregroove modulation, the disc information area being substantiallysmaller than the recordable area of the recording layer, and the discinformation areas of the recording layers being located at substantiallycorresponding radial positions.
 10. Device for scanning a track on arecord carrier (11) via a beam of radiation (24), the track comprisingmarks on a recordable area of a recording layer, the beam enteringthrough an entrance face of the record carrier and constituting ascanning spot having an effective diameter on the track, the recordcarrier comprising at least a first recording layer (40) and a secondrecording layer (41), the first recording layer being present at aposition closer to the entrance face than the second recording layer,and at least one transparent spacer layer (42) between the recordinglayers, and each layer comprising a pregroove indicating the position ofthe track, the pregroove exhibiting a wobble constituted bydisplacements of the pregroove in a direction transverse to thelongitudinal direction of the track, the wobble exhibiting a wobblemodulation for representing physical address information indicating thephysical position of the physical address with respect to a startingpoint of the track and the pregroove exhibiting a pregroove modulationconstituted by variations of a physical parameter related to the shapeof the pregroove, the pregroove modulation representing auxiliarycontrol information, the device comprising a head (22) for providing thebeam, a front-end unit (31) for generating a scanning signal (33) fordetecting marks in the track by detecting scanning signal variations dueto a first type of variations of the radiation, wobble detection means(36) for retrieving the physical address information from the wobblemodulation by detecting a second type of variations of the radiation,and pregroove demodulation means (32) for retrieving the auxiliarycontrol information from the pregroove modulation on the first and thesecond recording layer by detecting further scanning signal variationsdue to the first type of variations of the radiation.
 11. Device asclaimed in claim 10, wherein, while on the record carrier said markshave lengths corresponding to an integer number of channel bit lengths Tand the shortest marks having a length of a predefined minimum number dof channel bit lengths T for being detectable via the scanning spothaving the effective diameter, and the pregroove modulation isconstituted by a carrier pattern of long pregroove marks, the longpregroove marks having lengths of at least two times the predefinedminimum number d of channel bit lengths T for being substantially longerthan the effective diameter of the scanning spot, the pregroovedemodulation means (32) are arranged for detecting the further scanningsignal variations due to the long pregroove marks.
 12. Device as claimedin claim 10, wherein the pregroove demodulation means (32) are arrangedfor retrieving the auxiliary control information encoded in thepregroove modulation according to a predefined channel coding algorithm,which predefined channel coding algorithm differs from a channel codingalgorithm for encoding the information in the marks in the track. 13.Device as claimed in claim 10, wherein the device comprises a controlunit (20) for first retrieving the auxiliary control information via thepregroove demodulation means (32) and subsequently recording theauxiliary control information in a control area of the record carrier.